With the growth of air traffic, the aircraft ground traffic in airport areas is considerably intensified. Whether to get to a take-off runway entry from an embarkation point or to get to a debarkation point from a runway exit, the taxiing maneuvers in the airports today constitute difficult phases.
Various so-called “airport navigation” avionics functions have already been proposed to facilitate the movement on the ground of the aircraft in an airport context. For example, the map of the airport installations can be displayed on board, accompanied by relevant text information. This display can be complemented by various functions, such as a zoom to enlarge sectors defined by the pilot or such as route functions. The position of the airplane can also be displayed and alerts can be raised when the airplane begins a dangerous maneuver, such as an unauthorized approach to a runway, or a nonregulatory maneuver, such as the entry onto a runway in the reverse direction. The position of the other airplanes present on the site can also be displayed and anti-collision functions on the ground can be proposed.
Among the so-called “airport navigation” functions, the management of runway exits after landing to get to a taxiway is a critical task because it conditions both the good operation of the airport and the good operation of the aircraft. Runway occupancy times for landing that are longer than necessary are a source of waiting delays leading to an excess consumption of fuel for the aircraft in approach phase and a slowing down in the rate of landings.
Runway occupancy times that are longer than necessary are often caused by poor management of the runway exits. In practice, each landing runway has several exits, staged along the runway. Leaving the runway by taking one of the first exits reduces the occupancy time of the runway and also the quantity of fuel burnt in the landing phase, which is not inconsiderable bearing in mind that for a flight of approximately one hour, the quantity of kerosene consumed in taxiing can represent approximately 5% of the total quantity of kerosene consumed. However, optimizing the runway exit is not easy, because there are numerous parameters involved: the state of the surface of the runway, weather conditions, the weight and condition of the aircraft, in particular of the tires and of the braking system. Such is, moreover, why the runway exit is never planned, simply suggested. Furthermore, it is not enough to apply maximum braking to take the first exit, since the brakes can start to overheat which causes premature wear and compromises the profitability of the airplane.
The current solution consists, for the pilot, after the front landing gear has touched the ground, in initially reversing the thrust of the engines. Then, in a second stage, when the speed has passed below a certain speed threshold below which the brakes are effective, he operates the brake pedals acting on the wheels. The runway exit is chosen at a guess by the pilot, who visually estimates the first exit that he can reach at a speed less than or equal to the maximum speed allowable to take that exit. The maximum allowable speed to take an exit is the speed above which taking the exit presents a risk given the angle that the exit forms with the runway. This angle can range at least up to 90 degrees and the maximum speed reduces as the angle increases. Quite often, the pilot is forced to add supplementary thrust to get to a more distant exit because it is extremely improbable to reach an exit just at the moment when its maximum allowable speed is reached. By this method, clearly the safety conditions are given priority. In particular, in the case of a supplementary thrust, the problems of excess consumption of kerosene and excessive occupancy of the runways are largely disregarded.
The pilot can also be assisted by an automatic braking system, called “auto-brake”, which enables the pilot to select a deceleration level on an ascending scale ranging from 1 to 2, from 1 to 3 or from 1 to 5 depending on the airplane model. The system is started up immediately after the front landing gear has touched the ground and brakes the airplane to a complete stop in accordance with the deceleration level chosen by the pilot. The system is fixed and takes no account either of the particular landing conditions, such as the state of the runway or the weather conditions, or of the speed of the airplane when it touches down. It guarantees no stopping distance, the latter is variable even for a given deceleration level. It is up to the pilot to compensate for the lack of flexibility of the “auto-brake” system by taking over when he visually estimates that he can take an exit. For this, he simply has to operate the brake pedals to deactivate the system. The result is the same as for braking without the help of the “auto-brake” system: there is often a need to add supplementary thrust to get to a more distant exit. Economically, this solution is therefore not the best.
Moreover, during the landing, the pilot does not have any way of checking in advance that the length of runway remaining in front of his airplane is sufficient to complete his landing without overshooting the end of the runway. The availability of such information enables the pilot to judge sufficiently in advance if it is wise to go around to try a new approach.
The object of the invention is to optimize the occupancy time of a runway by an aircraft when landing and to optimize the fuel consumption after the wheels touch down. Its main aim is to avoid having to add supplementary thrust again to get to a more distant exit and to signal any risk of overshooting the end of the runway. When the front landing gear touches down, it is a matter of constantly estimating whether the deceleration level is appropriate and deducing from this if there is a need to increase or reduce the braking.
To this end, an object of the invention is a system and a method to assist in the braking of an aircraft on a landing runway.
The system comprises a means of acquiring the position of the aircraft on the runway and its speed in the taxiing phase, a means of storing data concerning the runway where the aircraft is landing and a predefined deceleration law. It also comprises a function for calculating the distance that the aircraft will have traveled on the runway when it has reached a certain speed and/or the speed that it will have reached when it has traveled a certain distance. The distance and/or the speed are calculated assuming that the speed of the aircraft decreases according to the stored deceleration law.
Advantageously, the storage means may contain the position characterizing a runway start or end point and the length of the runway. The calculation function may determine the distance to be traveled by the aircraft to reach a zero speed. The calculated distance makes it possible to adapt the braking by comparison with the distance remaining to reach the end of the runway.
Advantageously, again, the storage means may contain the position characterizing a runway start or end point, the length of the runway and the controlled speed of the aircraft below which it can perform any maneuver on the ground. The calculation function can determine the distance to be traveled by the aircraft to reach the controlled speed. The calculated distance makes it possible to adapt the braking by comparison with the distance remaining to reach the end of the runway. The controlled speed is generally a predefined value for the type of airplane concerned, such as 10 knots, for example.
Advantageously, again, the storage means may contain the position of the point characterizing a runway exit and the maximum speed to take that exit. The calculation function may determine the speed that the aircraft will have reached on the runway when it has traveled the distance to the exit. The calculated speed makes it possible to adapt the braking by comparison with the maximum speed to take the exit. The maximum exit speed can be a predetermined value, such as 30 knots, for example.
In a particular embodiment, the system may include an automatic braking module to increase or reduce the braking without the intervention of the pilot.
An audible alert module or a visual alert module may raise an alert if the stopping distance or the distance to reach the controlled speed of the aircraft is greater than the distance remaining to reach the end of the runway or if no exit can be reached at a speed less than or equal to its maximum exit speed.
A display module may be used to display the stopping distance or the distance to reach the controlled speed or even the speeds at the exits. The current position of the aircraft on the runway may even be graphically represented, as can the stopping distance or the distance to reach the controlled speed of the aircraft. The tendency to shorten or lengthen the stopping distance or the distance to reach the controlled speed of the aircraft may also be displayed graphically.
Advantageously, the exits may be graphically represented. If necessary, the graphic representation of an exit already passed can be different from the graphic representation of an exit not yet passed, or only the exits not yet passed can be graphically represented. If necessary, only the exits that can be reached at a speed less than their maximum exit speed are graphically represented, or the graphic representation of the exits that can be reached at a speed less than or equal to their maximum exit speed can be different from the graphic representation of the exits that cannot be reached at a speed less than or equal to their maximum exit speed.
A mechanism may prevent the jerking around of the moving graphic representations of the stopping distance or of the distance to reach the controlled speed of the aircraft, or even prevent the blinking of the fixed graphic representations of the exits that can be reached or not at a speed less than or equal to their maximum exit speed.
In one embodiment, the graphic representations of the exits may be different in automatic braking mode and in manual braking mode.
Another object of the invention is a method to assist in the braking of an aircraft on a landing runway. The method comprises a phase of recovering data concerning the aircraft or concerning the runway where the aircraft is landing, a phase of acquiring the position of the aircraft on the runway and its speed in the taxiing phase and a phase of calculating the distance that the aircraft will have traveled on the runway when it has reached a certain speed and/or the speed that it will have reached when it has traveled a certain distance. The distance and/or the speed are calculated assuming that the speed of the aircraft decreases according to a predefined time function.
Advantageously, the position characterizing the start or the end of the runway and the length of the runway are recovered in the data recovery phase and the distance that the aircraft will have traveled on the runway when it has reached a zero speed is calculated in the calculation phase, the calculated distance making it possible to adapt the braking by comparison with the distance remaining to reach the end of the runway. If necessary, this comparison is made visually by the pilot.
Advantageously, again, the position characterizing the start or the end of the runway, the length of the runway and the controlled speed of the aircraft below which it can perform any maneuver on the ground are recovered in the data recovery phase and the distance that the aircraft will have traveled on the runway when it has reached its controlled speed is calculated in the calculation phase. The calculated distance makes it possible to adapt the braking by comparison with the distance remaining to reach the end of the runway. If necessary, this comparison is made visually by the pilot.
Advantageously, again, the position characterizing a runway exit and the maximum speed to take this exit are recovered in the data recovery phase and the speed that the aircraft will have reached on the runway when it has traveled the distance to the exit is calculated in the calculation phase. The calculated speed makes it possible to adapt the braking by comparison with the maximum speed to take the exit. If necessary, this comparison is made visually by the pilot. In one particular embodiment, the position characterizing a runway exit and the angle that this exit makes with the axis of the runway are recovered in the data recovery phase, this angle making it possible to deduce a maximum speed to take this exit. The speed that the aircraft will have reached on the runway when it has traveled the distance to the exit is calculated in the calculation phase, the calculated speed making it possible to adapt the braking by comparison with the maximum speed to take the exit.
For example, the distance and/or the speed may be calculated assuming that the speed of the aircraft decreases according to a time-dependent function only, if necessary according to a linear time function. However, the distance and/or the speed may also be calculated assuming that the speed of the aircraft decreases according to a function depending on time and on other variables characterizing the instantaneous braking quality given the state of the runway or of the aircraft and being estimated when taxiing on this runway.
For example, again, the distance and/or the speed may be calculated by taking into account only the speed component along the axis of the runway. The axis of the runway may, for example, be determined by extraction from an airport database containing the position of the thresholds and of the ends of the runway or containing the geographic orientation of the runway. It may also be obtained by calculation based on the coordinates of notable points of the runway on which the aircraft is, such as the thresholds or the ends of the runway obtained from an airport database. More simply, the axis of the runway may be supplied by on-board systems.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious aspects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.